4 Answers
4

First, move or delete all your old photo libraries in Photos app for Mac. I deleted mine because I had 3rd party backups, obviously you shouldn't delete them if you don't. If you move it and it still doesnt show up, just hold the Option key while you start Photos.

Open it fresh, and it will say it can't locate your library. Click "Create New".. name it something like GARBAGE or DELETEME.

Then, go to settings and click 'set as system library', and also enable iCloud sync in settings (make your settings look like photo below). This will download all the photos fresh to this library (which doesnt have existing files so you dont have to worry about duplicates and such).

It will say "Updating X photos", make sure you wait for this step to finish.

However, when it starts saying "Downloading 10,000 photos" then you can move to the next step, you dont have to wait as long as it gets past the 'updating' step.

Select all with command+A, then delete. Go to your trash and then delete again by clicking Delete All.

It will still be stuck saying "downloading 10,000 photos" although they should now start deleting from iCloud (It took about 5 mins for me before it started removing them)

Once its done removing from iCloud web, just close Photos, and delete the temp library on your harddrive. From there, hold option when you start Photos and choose 'create new'. Youll be starting with a 100% fresh iCloud now.

This is how you mass delete photos from icloud.com without having to hold down "ctrl" and clicking each picture one by one, which could take forever.

Click the "moments" tab at the top center, so the photos are segregated by moments (location, date, etc).

On each moments section, look to the right hand side with your mouse pointer. You should see the addition "+" icon and the share icon (box with up arrow). Click on either icon.

By clicking either of these icons, the photos in that specific section will be highlighted blue. Just click any of the whitespace on the screen to not proceed with the sharing or adding action. The pop-up asking you if you want to add/share will disappear.

With the photos highlighted blue, click on the trash can icon at the top right hand corner to delete those pictures.

Repeat this process for each moments section until all photos are deleted.